The present invention relates in general to soil reinforcement fabrics and in particular to geotextile fabrics for reinforcing earthen structures.
Geotextile fabrics are commonly used to stabilize or reinforce earthen structures such as retaining walls, embankments, slopes and the like. Existing technologies include polyolefins (e.g., polypropylene and polyethylene) and polyesters which are formed into flexible, grid-like sheets. The sheets are stored on rolls whereby discrete lengths of the sheets are sequentially cut from the rolls and placed at the job site such that the higher strength warp strands thereof are disposed in a direction generally perpendicular to the face of the earthen structure.
Despite ease of manufacture and installation, polyolefin and polyester grids are low modulus of elasticity materials typically having Young""s moduli on the order of about 10,000 to about 75,000 psi for polyolefin grids and from about 75,000 to about 200,000 psi for polyester grids. Such low modulus products display high strain when subjected to the stresses in typical earthen structures. In some cases overlying soil and other forces associated with or imposed upon the earthen structure may induce as much as twelve inches of strain in polyolefin grids directions substantially transverse to the face of the earthen structure. Strains of this magnitude may destabilize not only the soil structure itself but also nearby structures such as buildings or roadways directly or indirectly supported by the soil structure.
Polyolefin grids may also undergo considerable creep when subjected to substantially constant loadings of the nature and magnitude of those typically exerted by or upon earthen structures. Thus, even if the short term strains are innocuous, the long term creep effects of polyolefin grids may be sufficient to threaten the integrity of the reinforced earthen structure and its surroundings.
Geotextile fabrics incorporating high modulus of elasticity materials have also been proposed for reinforcement of soil structures. These fabrics typically comprise elongate grid-like sheets wherein substantially parallel strands of high modulus material such as glass fiber rovings or the like extend in the longitudinal (or xe2x80x9cwarpxe2x80x9d or xe2x80x9cmachinexe2x80x9d) direction of the fabric and in the transverse (or xe2x80x9cweftxe2x80x9d or xe2x80x9ccross-machinexe2x80x9d) direction thereof. The glass strands are connected to one another so as to form an open grid and the entire assembly may be coated with a resinous material. The resinous material imparts a measure of semi-rigidity to facilitate handling of the fabric and protects the fabric from environmental degradation. Glass fiber roving strands have far higher moduli of elasticity and creep resistance than comparably sized polyolefin or polyester strands. For instance, the modulus of elasticity of a typical glass fiber strand in a geotextile fabric may be on the order of about 1,000,000 to about 4,000,000 psi. Glass strands can thus withstand much greater stress and undergo much less strain than comparably sized polyolefin or polyester strands. As such, glass-based geotextile fabrics generally provide superior reinforcement of earthen structures in relation to polyolefin or polyester grids.
Generally, soil movement is more likely to occur in a direction perpendicular rather than parallel to the face of an earthen structure. In selecting appropriate geotextile fabric reinforcement, therefore, a primary consideration is the minimization of soil movement transverse to the earthen structure""s face. It is thus essential that higher strength strands be disposed substantially perpendicular to the face of the earthen structure, whereas lower strength strands are generally suitable for disposition substantially parallel to the structure""s face.
Presently available geotextile fabrics possess higher strength strands in the warp direction of the fabric. In placing existing geotextile fabrics, a desired length of fabric is cut from a roll and laid such that the high strength warp strands extend perpendicular to the face of the earthen structure being constructed. Thereafter, another length of fabric is cut from the roll and placed adjacent to the first length of fabric with its high strength warp strands also extending perpendicular to the face of the earthen structure. The process of sequential cutting and placing of sections of fabric is repeated as necessary to substantially span the length of the face of the earthen structure. While the current practice of incremental placement of fabric sections produces acceptable end results, the process is unduly labor-intensive and time-consuming.
An advantage exists, therefore, for a unidirectional geotextile fabric which may be rapidly installed with minimal effort.
The present invention provides a unidirectional geotextile fabric for use in reinforcement of earthen retaining walls, embankments, slopes and related structures. The fabric comprises high modulus of elasticity strands extending in the weft direction of the fabric and comparatively lower modulus of elasticity yarn, thread or similar stitching material extending in the warp direction. The high modulus weft strands preferably comprise monofilament or bundled glass fibers which are connected to one another with heavy polyester warp yarn so as to establish an open grid fabric. The fabric is coated with a curable resinous material of sufficient thickness to protect the glass strands from damage as the fabric is rolled onto cores and unrolled at the job site. The resinous coating renders the fabric semi-rigid to thereby facilitate handling of the fabric and is of a composition suitable to resist moisture, abrasion and chemical degradation when the fabric is installed in an earthen structure.
When laying the fabric, a roll of the fabric is placed at one end of the face of the earthen structure being constructed and simply unrolled in a direction generally parallel to the structure""s face. Because the high modulus strands of the fabric are the weft strands they extend substantially perpendicular to the face of the structure. Hence, there is no need to cut and maneuver individual sections of the fabric to achieve desirable strand orientation, and installation time and effort are correspondingly reduced. Additionally, since the weft strands establish the width of the fabric, the fabric rolls may be easily manufactured or precut to any desired width to satisfy virtually any installation requirements.
Other details, objects and advantages of the present invention will become apparent as the following description of the presently preferred embodiments and presently preferred methods of practicing the invention proceeds.